1. Field of the Invention
The present invention relates to a programmable sequence controller capable of performing a desired sequence control under direction of a program which is made in accordance with a sequence circuit and written into a memory device.
2. Description of the Prior Art
Recently, it has been required in accordance with the complexity of a sequence control to provide a programmable sequence controller with a counting function that is capable of counting the number of ON-OFF changes in the state of a specified input/output element and detecting whether the counted number coincides with a set value. In order to have such a counting function, it may be necessary to provide a counting command as one of the commands of a sequence program and to enable an operation control device to execute such a counting command. In order to execute the counting command, it is necessary to provide a comparing function as well as an incrementing function to increment the counted value each time a specified input/output element has an ON-OFF change of state. For this reason, it is difficult to give a counting function to the operation control device in the sequence controller of the type which is only designed for executing a logic operation such as a test of an input/output element.
Another type of a programmable sequence controller contains a circuit therein for performing a counting function. However, this type stores the present value of the count of a counter and a set value in a memory, so that a program writing-in device and a special monitoring device have to be used for changing the set value and for monitoring the present value of the count of the counter and the set value. Furthermore, an operator has to memorize the location in the memory where the present value of the count of the counter and the set value are stored. Accordingly, it is difficult to monitor the present value of the count and the set value and to change the set value. The conventional program writing-in device and monitoring device can only represent one word of data stored in the memory, so that it is impossible to simultaneously monitor the present value of the count and the set value or the present values of the counts of a plurality of counters.